Unidirectional Path-switched Ring Research Articles

Maximum throughput traffic grooming in optical networks

In synchronous optical networks (SONETs) and WDM networks, low-rate traffic demands are usually multiplexed to share a high-speed wavelength channel. The multiplexing-demultiplexing is known as traffic grooming and is performed by SONET add-drop multiplexers (SADM). The grooming factor, denoted by k, is the maximum number of low-rate traffic demands that can be multiplexed into one wavelength channel. SADMs are expensive, and thus an important optimization problem for traffic grooming is to maximize the number of accommodated traffic demands subject to a given number of SADMs. We focus on the unidirectional path-switched ring (UPSR) networks with unitary duplex traffic demands. We assume that each network node is equipped with a limited number L of SADMs, and our objective is to maximize the number of accommodated traffic demands in a given set. We prove the NP-hardness of this maximum throughput traffic grooming problem and propose a (k+1)-approximation algorithm. Extensive simulations are conducted to validate the performance of the algorithm. We also study the all-to-all traffic pattern for the maximum throughput traffic grooming problem and propose an algorithm that accommodates at least (nL⌊k⌋)/2 demands for a UPSR with n nodes. We also prove that any optimal solution can accommodate at most (nLk)/2 demands. Thus the solution of our algorithm is at most a constant factor (approximately 2) away from the optimum.

On the complexity and algorithm of grooming regular traffic in WDM optical networks

In SONET/WDM networks, a high-speed wavelength channel is usually shared by multiple low-rate traffic demands to make efficient use of the wavelength capacity. The multiplexing is known as traffic grooming and performed by SONET Add-Drop Multiplexers (SADM). The maximum number of low-rate traffic demands that can be multiplexed into one wavelength channel is called grooming factor. Since SADMs are expensive, a key optimization goal of traffic grooming is to minimize the total number of SADMs in order to satisfy a given set of traffic demands. As an important communication traffic pattern, all-to-all traffic has been widely studied for the traffic grooming problem. In this paper, we study the regular traffic pattern, which is considered as a generalization of the all-to-all traffic pattern. We focus on the Unidirectional Path-Switched Ring (UPSR) networks. We prove that the traffic grooming problem is NP-hard for the regular traffic pattern in UPSR networks, and show that the problem does not admit a Fully Polynomial Time Approximation Scheme (FPTAS). We further prove that the problem remains NP-hard even if the grooming factor is any fixed value chosen from a subset of integers. We also propose a performance guaranteed algorithm to minimize the total number of required SADMs, and show that the algorithm achieves a better upper bound than previous algorithms. Extensive simulations are conducted, and the empirical results validate that our algorithm outperforms the previous ones in most cases. In addition, our algorithm always uses the minimum number of wavelengths, which are precious resources as well in optical networks.

The quantitative impact of survivable network architectures on service availability

This article presents results from research that included the modeling of various self-healing structures in order to compute the service availability between any two nodes within a given survivable network. In particular, terminal-pair availabilities are computed for a service-bearing transport signal that traverses a unidirectional path-switched ring (UPSR) system, a bidirectional line-switched ring (BLSR) system, a series of interconnected ring (UPSR and/or BLSR) systems, called a ring chain, within a general ring-based mesh network, and a series of interconnected point-to-point systems within a general point-to-point mesh network. In addition, these network structures are evaluated with varying degrees of fiber link and system interconnection node survivabilities; specifically, two-fiber and four-fiber link configurations are evaluated, and an intersystem nodal survivability factor a is used to characterize a transport signal of a given service level. Based on the results of these computations, several key observations are highlighted that should be considered when planning and designing short- and long-haul self-healing networks.